This disclosure relates to the bonding of polymer rings to metallic hubs, and, more particularly, to a process for manufacturing polymer/metal disks that are capable of being machined.
Various items (including gears, cam lobes, spacers, washers, flywheels, bushings, and pulleys) having a polymeric outer edge disposed around a metallic hub have previously been formed by multiple piece xe2x80x9cbatchxe2x80x9d processing methods. One method of multiple piece batch processing has heretofore involved adhesively disposing a tube of polymeric material over a steel billet to form a stock piece. The stock piece, which typically ranges in length from about six inches to about thirteen inches, is then sliced perpendicular to a longitudinal axis extending therethrough to produce disks of certain thicknesses having a polymeric ring disposed around a steel hub. Because of the variation in the degree of adhesion of the polymeric tube over the length of the steel billet, the degradation of the polymeric material, and the dimensional instability associated with cutting the stock piece to produce thin slices that are subsequently machined into finished pieces, the quality of finished pieces produced by such a method is generally poor. Furthermore, the opposing ends of the stock piece, or tailstocks, are usually scrapped. Moreover, the actual cutting of the stock piece results in lost material at the points at which the cuts are made. Scrapping of the tailstocks, the generation of xe2x80x9csawdustxe2x80x9d waste as a result of the cutting of the stock piece, and the proper disposal of all of the generated waste are factors that increase the cost of producing the finished pieces.
One method of single piece batch processing involves the casting of a polymer, such as nylon, directly onto a structural hub. Because in single piece casting methods each individual polymeric member must be separately molded onto the hub, time and space constraints typically hinder the manufacture of pieces by such a method. Additionally, during the solidification of the material, very high shrinkage occurs which results in high levels of undesirable residual stresses. These residual stresses are undesirable for strength and dimensional stability.
An additional method of single piece batch processing involves the injecting of a polymer, such as nylon, directly onto a structural hub using injection-molding techniques. Because in single piece injection molding methods each individual polymeric member must be separately injected onto the hub, materials are limited to those that are capable of being injection molded. Additionally, there are many attributes of injection molding that are undesirable, such as internal shrinkage porosity, knit lines, and anisotropic material behavior that could be undesirable for many applications.
A process for manufacturing machinable polymer/metal disks is disclosed herein. The process utilizes a single piece batch size concept that allows a ring/hub assembly to be efficiently produced for finishing into any one of a number of items. The process comprises applying a bonding agent to a metallic hub, pressing a polymeric ring over the metallic hub to form a ring/hub assembly, and heating the ring/hub assembly to cause bonding to occur between the polymeric ring and the metallic hub. The bonding agent is typically sprayed onto the metallic hub. Other methods, such as dipping of the metallic hub into the bonding agent or direct application of the bonding agent to the surfaces of the metallic hub, can also be employed. The bonding agent is generally an organosilane, although other compounds capable of bonding a polymer to a metallic substrate can be used. The pressing of the polymeric ring over the metallic hub typically comprises enlarging the polymeric ring either with heat or by stretching (or a combination of both heating and stretching) and mounting the enlarged polymeric ring over the metallic hub. The heating of the ring/hub assembly effectuates the softening of a surface layer of the polymeric ring to allow the softened polymer to flow into a textured surface of the metallic hub and harden, thereby retaining the polymeric ring on the metallic hub.
The foregoing process provides a practical solution to the problems associated with methods for manufacturing the polymer/metal disks of the related art. In particular, the single piece batch size manufacture of the polymer/metal disks allows near-zero rejection rates to be realized, utilizes less energy, and allows for the use of various types of polymeric materials and metallic hub designs to create a cost effective and high quality polymer/metal disk assembly that meets or exceeds the design specifications imposed for the manufacture of a finished product. Single piece manufacturing furthermore allows access to the process for the incorporation of monitoring equipment (e.g., temperature measurement devices and visual inspection instrumentation) to further promote process repeatability and provide opportunity for closed loop conditioning of the finished piece after the heating cycle is complete.